As conventional high-strength brass alloy used for a sliding member such as a bearing, can be mentioned the high-strength brass casting classes 1-4 prescribed in Japanese Industrial Standard JISH5120 (See Non-Patent Document 1). These high-strength brass alloys are obtained by adding elements such as Al, Fe, Mn and the like to Cu—Zn alloy to improve corrosion resistance in sea water, toughness, wear resistance and hardness, and used frequently for sliding applications such as a synchronizer ring in a transmission mechanism of an automobile, a gear wheel in an ordinary machine, and a bearing.
In the high-strength brass alloy, there appear various matrices such as α phase, β phase, α+β phase and γ phase according to zinc equivalents of added elements. When the zinc equivalent is smaller, α phase appears. Although the high-strength brass alloy in which α phase has appeared is superior in toughness, its hardness is inferior and, when put to sliding applications, easily shows abrasive wear. Further, when the zinc equivalent is increased, β phase appears. Then with further increase of the zinc equivalent, γ phase appears. The high-strength brass alloy in which γ phase has appeared has the advantages of increased hardness and improved wear resistance. But on the other hand, its toughness is significantly reduced and its shock resistance becomes lowered.
Thus, in the sliding applications, the high-strength brass alloy whose matrix is single phase of β phase is widely used since its toughness is not reduced and its wear resistance is superior. However, as efficiency and longer life of mechanical equipment are promoted recently, it is desired further to improve wear resistance of the sliding member of the high-strength brass alloy.
For improving wear resistance of the high-strength brass alloy having the matrix of α+β phase or β phase, is proposed the high-strength brass alloy having the matrix in which a manganese silicide type intermetallic compounds such as Mn5Si3 are dispersed (See Patent Document 1, for example), or the high-strength brass alloy having the matrix in which Fe—Mn—Si-based intermetallic compounds are dispersed (See Patent Documents 2 and 3, for example).